A majority of fuel cell systems developed to date use hydrogen and oxygen as anode and cathode feed respectively. Although hydrogen has a high energy density, a variety of alternative fuels have been investigated as fuels for transportation fuel cell systems, as they are safer to store and transport. In particular, methanol is the subject of several investigations (Kordesch and Simader, 1996, p. 151). Ammonia or hydrazine each has high power density, but requires safe handling (Kordesch and Simader, 1996, p. 333). Methanol or hydrocarbon fuels can be re-formed to hydrogen for use in standing or mobile power units (Kordesch and Simader, 1996, p. 297; Ziaka and Vasileiadis, 2000; Nakagaki et al., 2000). In each of these cases, the fuel is totally consumed for generation of hydrogen, that is then used to generate electrical power, and all carbon is converted to CO2.
In principle, the free energy change for any chemical reaction can be converted to electrical energy in an oxide ion conducting fuel cell (Scheme 1), if the required characteristics are present. A similar set of equations can be drawn for a fuel cell having a proton conducting membrane (Scheme 2), such as polymer electrolyte membrane fuel cells (PEMFC). In each case, suitable anode and cathode materials must be used to catalyze reactions 1 and 2. Partial oxidation of XH2 to X thereby provides free energy recoverable as electrical power. 
Any reaction in which a fuel (XH2 in Eqns. 1 and 3, Schemes 1 and 2) is oxidized to a value-added product (X in Eqns 1 and 3, Schemes 1 and 2) and energy, is a potential candidate for application in a fuel cell for co-generation of chemicals and power. One example of such a process is the production of sulfur from hydrogen sulfide.
Potential benefits from use of fuel cell technology for production of chemicals include improved selectivity and efficiency. An economic advantage is that there is a negative cost of feed for production of electrical power, as the cost of fuel is more than offset by the value of the product. In the case of conversion of H2S, the value of sulfur is not great. However, in this case use of a fuel cell-based process offers the potential economic advantage of reduced cost of treatment of sour gas streams. For other systems, for example when hydrocarbons are converted to products of significantly higher value, reduced cost for manufacturing the product can provide an economic incentive (Mazanec and Cable, 1990; Michaels and Vayenas, 1984; Petrovic et al., 2001; White et al., 2001)
H2S is a toxic and highly reactive pollutant. Removal of H2S from natural gas and process streams Is costly. The energy generated by oxidation of H2S to either sulfur, as in the Claus process, or SOx by combustion, is either vented or partly recovered as low-grade heat (Chuang and Sanger, 2000). There is a clear economic benefit to recovery of the heat of reaction of H2S to elemental sulfur as high-grade electrical energy.
Experimental SOFC's are known in which hydrogen sulfide can be oxidized; however no catalysts have yet been developed that are sufficiently active for fuel cell applications. In fact there are, at present, no commercial fuel cells for the production of sulfur from hydrogen sulfide.